Through-body duct

ABSTRACT

A vehicle comprising: a front surface exposed to the front of the vehicle; a forward ground-engaging wheel; a wheel arch defined by the body of the vehicle, the forward wheel being at least partially located in the wheel arch in at least one configuration of the wheel; and a duct extending from the front surface into the wheel arch, the duct being substantially unobstructed throughout its length.

This invention relates to a duct for channeling air in a road vehicle.

FIG. 1 is a front quarter view of a road vehicle. The vehicle has aforward-facing region shown at 1, and a front wing shown at 2. A frontroad wheel 3 is located in a wheel arch 4 which is defined at least inpart by the front wing. This region of the vehicle has two light units.A forward-facing light unit 5 is located in the forward-facing region 1.The forward-facing light unit contains a headlamp and a turn indicatorlamp. A side-facing light unit 6 is located in the wing 2. This providesturn indication to the side of the vehicle.

In some vehicles there is a heat exchanger or radiator 7 located at thefront of the vehicle. Some of the high energy air meeting the front ofthe vehicle when the vehicle is in motion passes through the heatexchanger, takes on heat from the heat exchanger, and can then beexpelled under the car or into one or both of the front wheel arches.The heat exchanger presents a substantial resistance to air passingthrough it. As a result, the air leaves it with relatively low energy.

When the vehicle is in forward motion, air will be deflected around thefront of the vehicle and will flow along the sides of the vehicle. Inorder for the vehicle to operate with aerodynamic efficiency, it isdesirable for the air flowing along the sides of the vehicle to remainattached to the vehicle. When the air flowing along the side of thevehicle meets the wheel 3 and the wheel arch 4 there is a tendency forit to be disrupted and to detach. It would be desirable to resist thistendency.

According to one aspect there is provided a vehicle comprising: a frontsurface exposed to the front of the vehicle; a forward ground-engagingwheel; a wheel arch defined by the body of the vehicle, the forwardwheel being at least partially located in the wheel arch in at least oneconfiguration of the wheel; and a duct extending from the front surfaceinto the wheel arch, the duct being substantially unobstructedthroughout its length.

The wheel may be a road wheel. The vehicle may be a road vehicle.

The duct may be free from obstructions extending across thecross-section of the duct. The duct may be free from radiators extendingacross the duct. The duct may be free from heat exchangers extendingacross the duct.

The duct may have an opening in the front surface. In the vehicle's Ydirection the opening may be wholly located further than 25% of themaximum width of the vehicle (at any point along the vehicle's length)from the vehicle's centreline. The front surface may include a frontlamp unit of the vehicle. The opening may be at least in part locatedimmediately outboard of the front lamp unit. The opening may be exposedat the front of the vehicle in a direction along the vehicle's X axis.

The vehicle may have a front wing. The front wing may define at least inpart the outboard wall of the duct. The front wing may extend rearwardlyto the wheel arch.

A single body panel may define at least part of the exterior surface ofthe front wing and the outboard wall of the duct. The material of thevehicle between the duct and the vehicle's exterior surface outboard ofthe duct may be solid and/or free from voids. This may be achieved if,for example, that material is constituted by a body panel.

The vehicle may comprises a side-mounted lamp unit whose outboardsurface is exposed at the exterior of the vehicle and whose inboardsurface defines at least in part the outboard wall of the duct.

The duct may have has an outlet into the wheel arch. That outlet may bein a wall of the wheel arch. At least part of that outlet may be locatednot more than 50 mm from the outboard leading edge of the wheel arch ona plane perpendicular to the vehicle's Z axis and running through thatpart of the outlet.

The vehicle may comprise a wheel cover located immediately outboard ofat least part of the wheel, the wheel cover being mounted so as not torotate with the wheel about the wheel's axis. The duct may be configuredso as to direct air flowing through the duct on to the outboard surfaceof wheel cover.

The duct may extends through the body of the vehicle. The vehicle may bean automobile.

The present invention will now be described by way of example withreference to the accompanying drawings. In the drawings:

FIG. 1 is a schematic front quarter view of a first road vehicle.

FIG. 2 is a schematic front quarter view of a second road vehicle.

FIG. 3 is a more detailed front view of the left part of the second roadvehicle from the front.

FIG. 4 is a view of the front part of the second road vehicle from theleft side.

FIG. 5 is a horizontal cross-section of part of the second road vehicle.

FIG. 6 is an exploded view of a wheel and associated components.

FIG. 7 is an exploded view of a wheel mounting structure.

FIG. 8 is an exploded view of a wheel and a hub cartridge.

FIG. 9 shows a wheel cover.

FIG. 10 is a side view of a wheel having a wheel cover.

FIG. 11 is a schematic view of a wheel cover with movable shutter.

The vehicle of FIGS. 2 to 5 has a forward-facing region shown at 11, anda front wing or wing panel shown at 12. A front road wheel 13 is locatedin a wheel arch 14 which is defined at least in part by the front wing.This region of the vehicle has two light units. A forward-directed lightunit 15 is located in the forward-facing region 11. The forward-directedlight unit contains a headlamp and a turn indicator lamp. A side-facinglight unit 16 is located in the wing 12. This provides turn indicationto the side of the vehicle. In the vehicle of FIG. 2, a duct 17 isdefined which runs through the body of the vehicle from a location inthe forward-facing region 11 adjacent the forward-facing lamp unit 15 toa location in the interior of the front wheel arch 14. The duct conveyshigh energy air from the front of the vehicle to the wheel arch 14. Thepresence of this high energy air in the interior of the wheel arch canhelp resist the separation of air flow from the side of the vehicle.

In more detail, the vehicle of FIGS. 2 to 5 is an automobile intendedfor road use. The vehicle has four road wheels, only one of which isshown in the figures. Any of the road wheels may be driveable (e.g. byan internal combustion engine and/or an electric motor) to cause thevehicle to move. The exterior of the body of the vehicle is defined by aset of body panels. Each body panel is a sheet element whose outersurface defines part of the exterior surface of the vehicle. The bodypanels may conveniently be made of a composite material such as a carbonfibre/resin composite, or of a metal such as aluminium or steel.

FIGS. 2 to 5 show part of the left side of the vehicle. The right sideis a mirror image.

Forward-facing region 11 defines the front-most part of the vehicle. Theforward-facing region includes a generally upright bumper or fender part20 and a splitter 21. Between the bumper part 20 and the splitter 21there are air inlets such as inlet 22. Air meeting the front of thevehicle can pass through these inlets and then through one or moreradiators or heat exchangers to cool operational parts of the vehicle.Because of the air resistance presented by the heat exchangers, oncethis air has passed through a heat exchanger it has relatively littlekinetic energy relative to the vehicle. Forward-facing region 11 alsoincludes forward-directed light units such as light unit 15. One ofthese units is located on either side of the car. Each of these unitsincludes at least one headlamp for illuminating the road in front of thevehicle. Each unit may also include a forward-directed turn indicatorand/or a daytime running lamp.

Lamp unit 16 is located on the front wing 12. It is directed to the sideof the vehicle. It may serve as a side repeater turn indicator or acontinuously illuminated side marker lamp.

The wing 12 is defined by a wing body panel. The wing body panel definesthe exterior surface of the upper flank or side edge 23 of the forwardpart of the vehicle. The wing body panel also defines the exteriorsurface of the vehicle below that edge, as indicated at 24. The wingbody panel may also define the upper surface of the forward part of thevehicle, as indicated at 25. The wing of the vehicle extends in alongitudinal direction from the forward-facing region 11 to at least theforward edge of the front wheel arch 14, and may extend to the forwardedge of the forward-most occupant door on the relevant side of thevehicle. The wing extends in a vertical direction from the lowest partof the side of the vehicle within the longitudinal extent of the wing tothe flank of the vehicle within that longitudinal extent. The wing isdefined by one or more wing body panels. Such panels may extend to otherregions of the vehicle: for example they may define part of theforward-facing region or part of the upper surface of the front of thevehicle.

As is shown in FIG. 3, the wing body panel is spaced outwardly from thepanel defining the bumper 20. This defines a gap 27 between the frontregion 11 of the vehicle and the panel(s) defining the side of thevehicle. That gap is open to the front of the vehicle. It forms theentrance 27 to the duct 17. The entrance may be located so that it isexposed directly to the front of the vehicle. At least part of theentrance may be located such that no part of the vehicle lies forward ofit on a line parallel with the vehicle's X axis and running through thatpart. The mean plane of the entrance 27 may be directed such that a lineperpendicular to that plane make an angle of less than 45° to thevehicle's X axis. As shown in FIG. 5, the remainder of the length of theduct 17 is defined between (i) a rearward continuation of the bumperstructure (this defines the majority of the inboard surface of the duct)and (ii) the wing body panel (this defines the majority of the outboardsurface of the duct). The inboard surface of the body of the duct isdefined by an outboard-facing surface 28 of a panel which is elongate inat least the vehicle's X direction. The outboard surface of the body ofthe duct is defined by an inboard-facing surface 29 of the wing panel.The upper and lower surfaces of the duct may be defined in anyconvenient way, but they may, for example be defined by the wing panel.The interior surfaces of the duct are preferably smooth and/or graduallycurved, so as to limit any reduction of the kinetic energy (relative tothe vehicle) of air passing through the duct. The duct is unobstructedby any radiator or heat exchanger. The duct has an exit 30. The exit 30opens into the wheel arch of the vehicle. The exit is located wholly orpredominantly inboard of the outer lip 40 (see FIG. 4) of the wheelarch. The exit communicates directly with the volume within the wheelarch. The exit may be wholly inboard of the wing of the vehicle on thesame side. The wheel arch is bounded at its forward lateral edge by therear edge of the wing panel (see 31 in FIG. 5) or by a structure carriedby the wing panel, such as lamp 16. The wheel arch is bounded at itsrear lateral edge by another body panel 32, which may conveniently formpart of an occupant door of the vehicle. It is preferred that all partsof the exit 30 of the duct lie within the bounds of the wheel arch. Itis preferred that the exit 30 of the duct is located so that, in atleast one condition of the vehicle, when the vehicle is in motion at aspeed greater than 100 km/h or greater than 150 km/h or greater than 200km/h in a straight line in still air at standard temperature andpressure (these will be referred to below as “reference conditions”) airexiting the duct will predominantly flow into the wheel arch.

FIG. 5 shows air flow through and around the duct 17. In FIG. 5 a tyreand a rim of the wheel 13 of the vehicle are shown at 33. Air meetingthe front 11 of the vehicle is pushed outwards, as shown generally at50. Some of that air passes around the exterior of the wing 12, as shownat 51. Some of the air meeting the front of the vehicle enters duct 17,as shown at 52. When the air passing around the exterior of the wingmeets the wheel arch 14 (i.e. immediately rearward of 31) there ispotential for that air to detach from the vehicle. That detachment wouldreduce the vehicle's aerodynamic efficiency. In the arrangement shown inFIG. 5, the high energy air exiting duct 17 into the wheel arch isconstrained in direction by the design of the duct 17. The duct 17forces that air to be directed with a vector that is predominantly ormore preferably strongly in the vehicle's X direction (e.g. such that inreference conditions the mean vector of that air as it exits the duct isoffset from the vehicle's X axis by less than 20°), towards the rear ofthe vehicle. That rearward flow of air meets the flow of air that haspassed over the exterior of the wing, and tends to energise the flow ofair that has passed over the exterior of the wing. This induces the flowof air that has passed over the exterior of the wing to remain attachedto the vehicle, as indicated at 53. This can narrow the vehicle's wakeand reduce the vehicle's drag.

It is preferred that the exit of 30 of the duct is located in the wheelarch and close to the outboard edge of the wheel arch. This can helpflow from the duct to meet the flow along the exterior of the wing. Forexample, in at least one X-Y plane of the vehicle, the offset in thevehicle's Y direction between the outboard edge of the duct's rearopening 30 and the forward outboard rim of the wheel arch may be lessthan 5 mm, 10 mm, 20 mm or 50 mm. That relationship may apply over morethan 30% or more than 60% of the height (in the vehicle's Z direction)of the duct's rear opening. The width of the duct in the vehicle's Ydirection may, for example, be between 50 mm and 100 mm over at least60% of the length (in the vehicle's X direction) of the duct. The heightof the duct may, for example, be between 15 mm and 30 mm over at least60% of the length of the duct. In the vehicle's X-Z plane the height ofthe duct may be at least 3 times or at least 5 times the width of theduct over at least 60% of the length of the duct. Ducts of thesedimensions may provide an effective high energy flow of air to theinterior of the wheel arch without greatly affecting the frontal area ofthe vehicle. The rim of the wheel arch may be a locus around which aplane tangent to the outer surface of the wheel arch makes an angle of45° to the wheel axis.

FIG. 5 shows that the rear of the light module 16 defines part of theinterior surface of the duct 17. The rear of the light module is exposedto air in the duct. This allows the light module to be cooled by air inthe duct.

At least part of the internal surface of the duct may be defined by theforward-facing lamp unit 15. That may be an inboard surface of the duct.At least part of the internal surface of the duct may be defined by theforward-facing lamp unit 16. That may be an outboard surface of theduct. The duct may be defined by multiple separate body panelcomponents. The inner surface of the duct may be defined by a bumpercomponent that forms a front-facing bumper of the vehicle. The outersurface of the duct may be defined by another component that is notintegral with the bumper component. That other component may be a wingcomponent of the vehicle which defines a wing of the vehicle. In adesign such as that shown in FIG. 3, that avoids the need for thematerial defining the exterior of the duct to extend substantiallyupwards from the body of the bumper.

The exit from the duct into the wheel arch may be directed onto theoutboard part of the wheel. The exit of the duct may be considered to bethe shape defined by the intersection duct with the wheelarch. Thecentrepoint of the exit of the duct may be located outboard of a planeperpendicular to the vehicle's Y axis that passes through the middle ofthe wheel's tyre in the vehicle's Y axis when the vehicle's steering isin its straight-ahead position. The centrepoint of the exit of the ductmay be located outboard of a plane perpendicular to the vehicle's Y axisthat is located 75% or 80% or 90% of the width of the tyre from theinboard edge of the tyre when the vehicle's steering is in itsstraight-ahead position. These features can assist in directing the airflow from the duct around the exterior of the wheel.

The wing panel that defines the lateral surface of the duct 17 mayterminate at its rearward end at the forward rim of the wheel arch intowhich the duct opens. The wing panel that defines the lateral surface ofthe duct 17 may define at least part of the upper surface of the frontof the vehicle, as shown at 25 in FIG. 3. The vehicle's panels may bedefined in any convenient manner. For example, in the description abovethe wing has been described as being defined by a wing panel. The wingpanel could be composed of multiple separate elements. The wing of thevehicle may be defined by multiple panels. A different panel may definethe lateral surface of the duct from any which defines the exteriorsurface of the vehicle.

FIGS. 6 to 9 show aspects of a wheel structure. This wheel structure canitself provide advantages by itself, but it has been found to beparticularly advantageous in conjunction with the duct described above.

The wheel structure is shown generally in FIG. 6. The wheel structurecomprises a mounting arrangement 60, a hub cartridge 61, a road wheel 62and a wheel cover 63. The mounting arrangement mounts the wheel to avehicle. It can permit rotation of the wheel relative to the vehicleabout the wheel's central axis 64 and about a steering axis 65. Inpractice the steering axis is roughly vertical (e.g. within 20° of thevehicle's Z axis when the structure is attached to a vehicle). As willbe described in more detail below, the hub cartridge is attached to thecentre of the wheel. The hub cartridge has a core 66 which is free torotate relative to the wheel about the wheel axis 64. The wheel cover 63is attached to the core 66. A rigid reaction link 67 extends from thebody of the mounting arrangement to the core 66. The reaction linkengages the core and prevents it rotating as the wheel spins. In thatway the wheel cover is prevented from spinning with the wheel,

The wheel structure will now be described in more detail.

FIG. 7 shows the mounting arrangement. The mounting arrangementcomprises a body 68. The body is a rigid component which attaches bymounts 69 to a vehicle's body. Mounts 69 are arranged to permit rotationof the mounting body 68 relative to the vehicle's body about thesteering axis 65. The steering axis runs through the mounts 69. Themounting body has an attachment point 70 for a steering arm which cancause the body to rotate about the steering axis. A wheel bearing islocated between the mounting body and a wheel carrier 71. The wheelbearing permits the wheel carrier to rotate freely about its axisrelative to the mounting body. The wheel carrier has a series of holes72 for receiving wheel bolts whereby the wheel 62 can be attached to thewheel carrier. The wheel carrier could alternatively have a series ofthreaded studs onto which the wheel can be tightened by means of wheelnuts. Once the mounting body is attached to the body of a vehicle andthe wheel is attached to the wheel carrier, the wheel is attached to thevehicle such that it can (i) spin relative to the mounting body aboutits own axis 64 by virtue of the wheel bearing and (ii) rotate with themounting body and relative to the body of the vehicle about the steeringaxis 65.

The wheel carrier 71 rotates with the wheel. The wheel carrier has ahole extending through its centre. The wheel bearing has a holeextending through its centre. The mounting body 68 has a through-hole 73aligned with the through-holes in the wheel carrier and the wheelbearing. As a result, when the wheel is mounted on the wheel carrier,the centre region of the wheel is accessible along the wheel's axis 64from the inboard side of the mounting body 68. (That is the side fromwhich it is viewed in FIG. 7).

The mounting arrangement comprises the reaction link 67. The reactionlink is a rod which is sized to pass through the hole 73 in the mountingbody and the corresponding holes in the wheel bearing and the wheelcarrier. At its inboard end the reaction link is rigidly attached to aspider 74. The spider is a rigid component which extends radiallyoutward from the reaction link. The reaction link is rigidly attached tothe mounting body by the spider. It will be appreciated that thereaction link could be attached to the mounting body by any suitablestructure: for example it could have a splined fit to the hole 73.

Turning to FIG. 8, the wheel has a series of holes 75 whereby it can beattached to the wheel carrier. Other forms of wheel mounting could beused. The centre of the wheel has a through-hole 76. The hub cartridge61 has an outer sleeve 76 and an inner shaft or core 66. The inner shaftis mounted to the outer shell by bearings so that the inner shaft iscapable of revolute motion with respect to the outer shell. Preferablythese are roller bearings, or two spaced-apart races of ball bearings,so as to resist tilting of the inner shaft perpendicular to the wheelrotation axis. This can help to reduce play of the cover relative to thewheel rim when the cover is attached to the inner shaft as will bediscussed below. The outer shell is shown separated from the wheel inFIG. 8 but in use the outer shell is rigidly attached to the wheel withthe inner shaft 66 through the through-hole 76 and the rotation axis ofthe inner shaft aligned with the rotation axis of the wheel. The innershaft 66 could be linked by a bearing directly to the body of the wheel,the body of the wheel being integral with the wheel spokes andoptionally the wheel rim. However, it is advantageous if the hubcartridge has the sleeve 76 containing the bearing and if that sleeve isremovable from the wheel, preferably by means of hand tools. This canassist with tyre fitment and wheel balancing. It may be advantageous forthe outer surface of the sleeve 76 to be a taper fit in the hole inwhich it fits in the centre of the wheel. This can be achieved if one orboth of the interior of that hole and the exterior of the sleeve is/aretapered so that the two come into contact as the sleeve is brought homein the hole. This permits the sleeve to be self-centring with respect tothe wheel when the two are assembled together.

The wheel cover 63 has generally the form of a plate. At the centre ofthe wheel cover is a fixing 78. The fixing is arranged so it can attachthe cover rigidly to the inner shaft 66. For example, the fixing maycomprise a bolt which can be screwed into a threaded hole in theoutboard end of the inner shaft. The fixing can attach the cover to theshaft in such a way that the cover is rotationally fast with the shaftabout the wheel axis 64. This may be achieved by there being positiveengagement between the shaft and the fixing (e.g. a spline) and/or bythe fixing being tightened to the shaft (e.g. by a threaded fastener).The wheel cover is conveniently rigid, so that it does not flex when thevehicle is under way.

The inner shaft 66 is configured on its inboard end so it can mate withthe outboard end of the reaction link 67 in such a way that the reactionlink is rotationally fast with the inner shaft about the rotation axis64 of the wheel. The inner shaft is also configured so that that matingcan be achieved by bringing the inner shaft and the reaction linktogether in a direction along the rotation axis 64 of the wheel. In theexample shown in the figures, these properties are achieved by providingthe reaction link with a slot 78 which runs radially in its outboardend, and providing the inner shaft 77 with a rib 79 which runs radiallyin its inboard end. When the hub cartridge is attached to the wheel andthe wheel is attached to the wheel carrier, the rib 79 is located in theslot 78. The sides of the rib bear on the sides of the slot, preventingrelative rotation of the inner shaft 77 and the reaction link about thewheel axis. Thus the rib and slot define a clevis joint. The rib and theslot could be reversed, so that the rib is on the reaction link and theslot is on the inner shaft 77. Other structures could be used to providea similar effect: for example one of (i) the inboard end of the innershaft and (ii) the outboard end of the reaction link could be a splinedfit in the other. An advantage of the clevis joint as shown in thefigures is that it can permit some angular rotation of the inner shaftrelative to the reaction link about axes perpendicular to the wheelaxis. Rotation of that nature might take place due to compliance in thewheel bearing when the wheel is under high bump, rebound, accelerationor deceleration load. This play between the inner shaft and the reactionlink reduces the extent to which that rotation is transmitted to thereaction link.

To assemble the wheel structure, the mounting structure 60 is attachedto the body of the vehicle. The hub cartridge is attached to the wheel.Then the wheel can be attached to the wheel carrier. Because the innershaft 77 of the hub cartridge can mate with the reaction link thoughmotion along the wheel axis, the inner shaft and the reaction link canbe mated through the action of offering the wheel up to the wheelcarrier. (The inner shaft 77 might first have to be rotated to aposition where it will interlock with the reaction link). Then the wheelcan be bolted or otherwise attached to the wheel carrier. The wheelcover can then be fixed to the inner shaft 77.

Once the wheel structure is assembled, the wheel is free to rotate aboutits axis with respect to the vehicle, but the wheel cover—despite beingmounted outboard of the wheel—is restrained from rotating about thewheel's axis. The wheel cover is restrained about that axis because itis fixed to the inner shaft, which in turn is stopped from rotating bythe reaction link. On the other hand, the wheel cover will rotate withthe wheel when the wheel is moved about its steering axis. It ispreferred that the reaction link is sized so that it is spaced from themounting body, the wheel bearing and the wheel carrier where it passesthrough them. This reduces the likelihood of the reaction link passingload in vehicle X or Z from the wheel to the mounting structure.

The wheel cover can have a generally smooth exterior surface. When sucha wheel cover is in place, it can reduce the drag resulting from thewheels. One reason for this effect may be that airflow past the exteriorof the wheel is more likely to remain attached to the exterior of thevehicle. This may reduce the width of the vehicle's wake. This effectcan be promoted by the fact that the surface presented to the passingair in the outer centre of the wheel is not rotating. It can also bepromoted if the wheel cover sits close to the wheel rim. For example,over at least 50% of the circumference of the wheel rim the spacingbetween the radially outermost part of the wheel cover and the closestlocation on the wheel rim may be less than 10 mm or less than 5 mm. Itis possible that the wheel cover or its mountings may flex, especiallywhen the vehicle is at high speed. One potential advantage of themounting system described above is that the cover can be held fixed in arelatively secure manner relative to the wheel rim. In an alternativeembodiment the wheel cover could be attached directly to the outboardend of the reaction link, and the hub cassette could be omitted.However, in some applications that may provide less control over thelocation of the wheel cover than if the hub cassette is used.Conveniently, the periphery of the cover may be located inward withrespect to the wheel axis of the innermost part of the tyre that isexposed at the side of the wheel. The tyre may flex during driving,which may otherwise alter the clearance between the cover and the wheel.Conveniently, the majority of the length of the periphery of the coveroverlies the rim of the wheel in a projection parallel to the wheelaxis. This can help to maintain an accurate clearance between the coverand the wheel.

The configuration of the wheel cover will now be described.

In the description below potential locations for cut-outs or holes inthe cover will be described. Where the context permits, these cut-outsor holes may be at the periphery of the cover or within the periphery ofthe cover When a cut-out or hole is at the periphery of the cover, theperiphery of the cover defines part of the periphery of the hole orcut-out, and the remainder of the periphery of the cut-out or hole isdefined by the continuation of the curve of the outer rim of the coverfrom its inflection on one side of the cut-out or hole to its inflectionon the other side of the cut-out or hole. That curve may be a circle.Such a circle may have the centre of the cover and/or the wheel axis(when the cover is in place over a wheel) as its centre. When a cut-outor hole is within the periphery of the cover, the periphery of thecut-out or hole does not intersect the periphery of the cover and thecut-out or hole is encircled by material of the cover.

In one example, the wheel cover has a circular rim extending around itsentire periphery and a flat or convex dished outer surface. This canassist in reducing drag. In some vehicles, for examplemoderate-performance vehicles or vehicles whose brakes perform better athigh temperatures, this may be optimal. In other vehicles it may beadvantageous to provide one or more passages whereby air may readilyflow past the wheel cover between the interior of the wheel (i.e. theregion bounded by the wheel rim) and the exterior. One advantage of thismay be to allow hot air in the interior of the wheel to escape, coolinga brake unit located in the interior of the wheel. Another advantage maybe to reduce the lift that may be generated by air spinning in theinterior of the wheel. One way to provide such a passage is to configurethe cover so that its rim describes only a partial circle. A cut-out maybe provided in the remainder of the cover. Thus, the cover may be in theform of a circle having a region missing from its periphery.Alternatively, a through-hole may be provided through a part of thecover such that the hole is surrounded by material of the cover.

FIG. 10 shows some potential locations for such a cut-out or hole. InFIG. 10 the wheel comprises a rim 80 attached to a hub 81 by spokes 82.A tyre 83 is located around the rim. A cover 84 is located over theexterior of the wheel. As described above, over the majority of thecircumference of the rim the periphery of the cover lies close to therim. The majority (see 85) of the periphery of the cover lies on acircle about the wheel's rotation axis. Part of the periphery of thecover lies inside that circle. That part of the periphery of the coverdefines a cut-out 86. Defining a hole through the cover as a cut-out(i.e. with no part of the cover directly outboard of that hole withrespect to the wheel axis) is convenient because it avoids there beingrelatively narrow outboard parts of the cover which might flex or beeasily broken.

In FIG. 10, the forwards direction of travel of the vehicle is shown at87. Quadrants of the wheel are shown at 88-91. A hole through the cover(e.g. a cut-out as described above) may be located anywhere around thecover. Some preferred factors bearing on the location of the cut-out orhole are:

-   -   It may be advantageous for the cut-out or hole to be wholly or        predominantly located in the rear or downstream quadrants 89,        90. Locating a substantial part of the cut-out or hole in the        forward or upstream quadrants 88, 91 may increase drag over        locating the cut-out or hole substantially in the downstream        quadrants. Conveniently greater than 50% or greater than 75% or        100% of the total area of hole(s) though the cover (as projected        onto a plane perpendicular to the wheel axis) is located in the        downstream quadrants 89, 90.    -   It may be advantageous for the cut-out or hole to be wholly or        predominantly located in the upper quadrants 88, 89. Locating a        substantial part of the cut-out or hole in the upper quadrants        may facilitate brake cooling by convection. Conveniently greater        than 40% of the total area of cut-out(s) or hole(s) though the        cover (as projected onto a plane perpendicular to the wheel        axis) is located in the upper quadrants 88, 89.    -   It may be advantageous for the cut-out or hole to be located so        that it partly or wholly overlaps a brake calliper 92 of the        wheel, when the two are projected onto a plane perpendicular to        the wheel axis. This can help heat to escape the calliper by        radiation. It has been found that preferred characteristics of        the cut-out(s) or hole(s) through the cover, any of which may be        adopted individually or in combination are:

1. for the hole or cut-out to be located at the periphery of the cover;

2. for 100% or more than 90% of the total area of the hole(s) asprojected onto a plane perpendicular to the wheel axis to be locateddownstream of the wheel axis in the plane.

3. for 50% or more than 40% of the total area of the hole(s) asprojected onto a plane perpendicular to the wheel axis to be locatedabove the wheel axis in the plane;

4. for 50% or more of the projection of a brake calliper of the wheelonto a plane perpendicular to the wheel axis to be overlapped by thehole(s).

The area of a hole located at the edge of the cover may be determined bytaking the circumferential continuation of the outer rim of the coverwith constant radius from the points where the hole deviates from thatrim to define the outer edge of the hole.

The cover may be configured so that it has one or more through-holes(which may or may not be at the periphery of the cover) and a mechanismwhereby one or more of those holes can be selectively opened or closed.For example, there may be a shutter located immediately inboard of thecover which can be rotated (e.g. by means of a motor or a linearactuator) relative to the cover to close the hole(s). The mechanism maybe actuated to open the hole(s) in response to a command from a driverof the vehicle or dependence on one or more predetermined conditions.For example, the shutter could be actuated to close the hole(s) when thevehicle exceeds a predetermined speed and to subsequently open thehole(s) when the vehicle brakes. Alternatively, the shutter could beactuated to open the hole(s) when the temperature of the wheel's brakeexceeds a predetermined threshold. FIG. 11 shows such a wheel cover fromthe inboard side. The wheel cover 96 has a hole in the form of aperipheral cut-out 97. A shutter 98 is mounted to the cover 96 by a pin93 about which it can rotate relative to the cover. A linear actuator 94carried by the cover can be operated to cause the shutter to movebetween a first position (as shown in FIG. 11) in which the hole isunobscured and a second position (as shown by the dotted line at 95) inwhich it closes the hole.

A vehicle may be provided with a static wheel cover of the typedescribed with reference to FIGS. 6 to 11 and a duct of the typedescribed with reference to FIGS. 2 to 5. The duct may be configured todirect air from its outlet in the wheel arch on to the leading edge ofthe wheel cover. This is particularly effective in reducing drag becausethe static wheel cover can better encourage air flow to stay attached tothe vehicle than a wheel with no cover or a wheel with a rotating cover.The duct may be configured to direct air at a tangent to the exteriorsurface of the wheel cover. The duct may be configured so that, in atleast one condition of the vehicle, when the vehicle is in motion at aspeed greater than 100 km/h or greater than 150 km/h or greater than 200km/h in a straight line in still air at standard temperature andpressure the majority of the air flowing through the duct is directed(i) to the exterior surface of the wheel cover and/or (ii) to passwithin 20 mm of the exterior surface of the wheel cover.

The applicant hereby discloses in isolation each individual featuredescribed herein and any combination of two or more such features, tothe extent that such features or combinations are capable of beingcarried out based on the present specification as a whole in the lightof the common general knowledge of a person skilled in the art,irrespective of whether such features or combinations of features solveany problems disclosed herein, and without limitation to the scope ofthe claims. The applicant indicates that aspects of the presentinvention may consist of any such individual feature or combination offeatures. In view of the foregoing description it will be evident to aperson skilled in the art that various modifications may be made withinthe scope of the invention.

1. A vehicle comprising: a front surface exposed to the front of thevehicle; a forward ground-engaging wheel; a wheel arch defined by thebody of the vehicle, the forward wheel being at least partially locatedin the wheel arch in at least one configuration of the wheel; and a ductextending from the front surface into the wheel arch, the duct beingunobstructed throughout its length.
 2. A vehicle as claimed in claim 1,wherein the duct is free from obstructions extending across thecross-section of the duct.
 3. A vehicle as claimed in claim 1, whereinthe duct has an opening in the front surface and in the vehicle's Ydirection the opening is wholly located further than 25% of the maximumwidth of the vehicle from the vehicle's centreline.
 4. A vehicle asclaimed in claim 1, wherein the duct has an opening in the frontsurface, the front surface includes a front lamp unit of the vehicle andthe opening is located immediately outboard of the front lamp unit.
 5. Avehicle as claimed in claim 1, wherein the vehicle has a front wing, andthe front wing defines at least in part the outboard wall of the duct.6. A vehicle as claimed in claim 5, wherein a single body panel definesat least part of the exterior surface of the front wing and the outboardwall of the duct.
 7. A vehicle as claimed in claim 1, wherein thevehicle comprises a side-mounted lamp unit whose outboard surface isexposed at the exterior of the vehicle and whose inboard surface definesat least in part the outboard wall of the duct.
 8. A vehicle as claimedin claim 1, wherein the duct has an outlet into the wheel arch and atleast part of the outlet is located not more than 50 mm from theoutboard leading edge of the wheel arch on a plane perpendicular to thevehicle's Z axis and running through that part of the outlet.
 9. Avehicle as claimed in claim 1, wherein the vehicle comprises a wheelcover located immediately outboard of at least part of the wheel, thewheel cover being mounted so as not to rotate with the wheel about thewheel's axis, and the duct is configured so as to direct air flowingthrough the duct on to the outboard surface of wheel cover.
 10. A ductas claimed in claim 1, wherein the duct extends through the body of thevehicle.
 11. A vehicle as claimed in claim 4, wherein the vehicle has afront wing, and the front wing defines at least in part the outboardwall of the duct.
 12. A vehicle as claimed in claim 11, wherein a singlebody panel defines at least part of the exterior surface of the frontwing and the outboard wall of the duct.
 13. A vehicle as claimed inclaim 4, wherein the vehicle comprises a side-mounted lamp unit whoseoutboard surface is exposed at the exterior of the vehicle and whoseinboard surface defines at least in part the outboard wall of the duct.14. A vehicle as claimed in claim 11, wherein the vehicle comprises aside-mounted lamp unit whose outboard surface is exposed at the exteriorof the vehicle and whose inboard surface defines at least in part theoutboard wall of the duct.
 15. A vehicle as claimed in claim 12, whereinthe vehicle comprises a side-mounted lamp unit whose outboard surface isexposed at the exterior of the vehicle and whose inboard surface definesat least in part the outboard wall of the duct.
 16. A duct as claimed inclaim 4, wherein the duct extends through the body of the vehicle.